best distortion plug

sorry if this has already been discussed...
i'm looking for a good distortion plug-in, or an amp-modeler that
essentially can function as such. something that can produce a heavy,
fuzzy guitar-type distortion, though i'm going to use it for other
instruments obviously.
anyone had any good experiences with such a thing? in my experience
it's one of the harder good plug-in types to find.
thanks for any advice/comments!
-3nki